1. Field of the Invention
Embodiments of the present invention relate to an organic light emitting display device and a method for driving the same. More particularly, the present invention relates to an organic light emitting display device that compensates degradation of an organic light emitting diode, and a method for driving the same.
2. Discussion of the Related Art
With recent development in multimedia, there is an increasing demand for flat panel displays. In order to satisfy this increasing demand, various flat panel displays such as liquid crystal display device, plasma display panel, field emission display device and organic light emitting display device are practically used. Among the various flat panel displays, the organic light emitting display device has been attractive as a next-generation flat panel display owing to advantages of rapid response speed and low power consumption. In addition, the light emitting display can self-emit light, whereby the light emitting display does not cause a problem related with a narrow viewing angle.
Generally, the organic light emitting display device may include a display panel having a plurality of pixels, and a panel driver for driving the respective pixels so as to make the respective pixels emit light. In this case, the pixels are respectively formed in pixel regions, wherein the pixel regions are defined by crossing a plurality of gate lines and a plurality of data lines.
Referring to FIG. 1, each pixel may include a switching transistor (Tsw), a driving transistor (Tdr), a capacitor (Cst), and an organic light emitting diode (OLED).
As the switching transistor (Tsw) is switched by a gate signal (GS) supplied to a gate line (GL), a data voltage (Vdata) supplied to a data line (DL) is supplied to the driving transistor (Tdr).
As the driving transistor (Tdr) is switched by the data voltage (Vdata) supplied from the switching transistor (Tsw), it is possible to control a data current (Ioled) flowing to the organic light emitting diode (OLED) by a driving voltage (VDD).
The capacitor (Cst) is connected between gate and source terminals of the driving transistor (Tdr), wherein the capacitor (Cst) stores a voltage corresponding to the data voltage (Vdata) supplied to the gate terminal of the driving transistor (Tdr), and turns-on the driving transistor (Tdr) by the use of stored voltage.
The organic light emitting diode (OLED) is electrically connected between the source terminal of the driving transistor (Tdr) and a cathode electrode applied with a cathode voltage (VSS), wherein the organic light emitting diode (OLED) emits light by the data current (Ioled) supplied from the driving transistor (Tdr).
Each pixel of the organic light emitting display device according to the related art controls an intensity of the data current (Ioled) flowing to the organic light emitting diode (OLED) by the driving voltage (VDD) through the use of switching of the driving transistor (Tdr) according to the data voltage (Vdata), whereby the organic light emitting diode (OLED) emits light, thereby displaying an image.
However, the organic light emitting diode (OLED), which is necessarily required for the above organic light emitting display device according to the related art, corresponds to an organic matter. Thus, the organic light emitting diode (OLED) is gradually degraded in accordance with the electrical stress and the elapse of time. This degradation of the organic light emitting diode (OLED) may have the nonlinear characteristics, and a level of the degradation may vary depending on the electrical stress. Thus, luminance variations in the neighboring pixels may cause un-uniformity of luminance. Especially, after driving the organic light emitting display device for a long time, a residual image may happen due to the degradation of the organic light emitting diode (OLED).
FIGS. 2 and 3 illustrate luminance changes of the organic light emitting display device according to the related art. FIG. 2 illustrate first to third pixels (P1, P2, P3) to which the different electrical stresses are respectively applied. FIG. 3 is a graph illustrating the luminance changes in the respective first to third pixels (P1, P2, P3), shown in FIG. 2, in accordance with the elapse of time (hours).
In FIG. 2, supposing that the electrical stress applied to the third pixel (P3) is higher than the electrical stress applied to the first and second pixels (P1 and P2), and the electrical stress applied to the first pixel (P1) is higher than the electrical stress applied to the second pixel (P2). As shown in FIG. 3, the respective first, second and third pixels (P1, P2, P3) have the different luminance changes. That is, the luminance change in the third pixel (P3) applied with the highest electrical stress is relatively larger than the luminance change in the first and second pixels (P1 and P2) in accordance with the elapse of time (hours). Due to the variations in the luminance changes of the respective pixels (P1, P2, P3), even though the data voltage is identically applied to the first, second and third pixels (P1, P2, P3), the luminance various may occur due to the degradation variations.
In the organic light emitting display device according to the related art, it is difficult to realize the uniform luminance due to the luminance variations which are caused by the degradation variations. Furthermore, picture quality may be deteriorated due to the residual image by the luminance variations.